Generally, a metal line of a semiconductor device connects circuits formed within a semiconductor substrate by providing an electrical connection between one or more semiconductor devices and a pad connection. The metal line typically comprises a metal thin film such as an aluminum film, an aluminum alloy film, and/or a copper film.
In forming such a metal line, in order to connect electrodes and pads that are separated by an insulating layer such as an oxide layer, a contact hole is previously formed by selectively etching the insulating layer. A metal plug filling the contact hole is then formed using a barrier metal and tungsten. In addition, a metal line for connecting electrodes and pads is formed by forming a metal thin film at an upper portion of the semiconductor device and patterning it.
A photolithography process is typically used for the patterning of such a metal line. However, it is difficult to form a sufficiently fine pattern of a metal line because of the recent trend of decreasing the CD (critical dimension) of the metal line as semiconductor devices become more miniaturized. Therefore, in order to solve this problem, a damascene process has been introduced to easily form a metal line with a fine pattern.
The damascene process forms a fine metal line layer by: (a) depositing an upper insulating layer such as an oxide layer above an insulating layer after forming a tungsten plug within a contact hole of an insulating layer, (b) removing a portion of the upper insulating layer in a region where a metal line pattern is formed by a photolithography process, (c) depositing a metal thin film thereabove, and then (d) performing a CMP (chemical mechanical polishing) process and planarizing the metal thin film.
However, a seam may be formed in the metal line formed by such a damascene process. This seam may be formed during the deposition of the metal thin film. That is, an empty space that is not filled with a metal thin film when the metal thin film is filled in a contact hole and a trench may be formed, because the contact hole of the interlayer insulating layer and the trench of the insulating layer may have a greater depth than width. This empty space becomes a seam of the metal line. Such a seam may deteriorate the electrical characteristics and reliability of a semiconductor device associated with the metal line.